linux-kernel - Re: [cgroup or VFS ?] WARNING: at fs/namespace.c:636 mntput_no

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Date:	Fri, 13 Feb 2009 14:31:12 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	containers@...ts.osdl.org, LKML <linux-kernel@...r.kernel.org>,
	Paul Menage <menage@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [cgroup or VFS ?] WARNING: at	fs/namespace.c:636	mntput_no_expire+0xac/0xf2()

Li Zefan wrote:
> Al Viro wrote:
>> On Fri, Feb 13, 2009 at 01:09:17PM +0800, Li Zefan wrote:
>>
>>> I ran following testcase, and triggered the warning in 1 hour:
>>>
>>> thread 1:
>>> for ((; ;))
>>> {
>>>         mount --bind /cgroup /mnt > /dev/null 2>&1
>>>         umount /mnt > /dev/null 2>&1
>>> }
>>>
>>> tread 2:
>>> for ((; ;))
>>> {
>>>         mount -t cgroup -o cpu xxx /cgroup > /dev/null 2>&1
>>>         mkdir /cgroup/0 > /dev/null 2>&1
>>>         rmdir /cgroup/0 > /dev/null 2>&1
>>>         umount -l /cgroup > /dev/null 2>&1
>>> }
>> Wow.  You know, at that point these redirects could probably be removed.
> 
> Ah, yes.
> 
>> If anything in there ends up producing an output, we very much want to
>> see that.  Actually, I'd even make that
>> 	mount --bind /cgroup/mnt || (echo mount1: ; date)
>> etc., so we'd see when do they fail and which one fails (if any)...
>>  
>> Which umount has failed in the above, BTW?
>>
>>
> 
> the first one sometimes failed, and the second one hasn't failed:
> 

Just triggered the warning at about:
	Fri Feb 13 14:26:03 CST 2009

But both 2 threads were not failing at that time:

mount: wrong fs type, bad option, bad superblock on /cgroup,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

mount1
Fri Feb 13 14:25:21 CST 2009
umount: /mnt: not mounted
mount: wrong fs type, bad option, bad superblock on /cgroup,
...

mount1
Fri Feb 13 14:26:32 CST 2009
umount: /mnt: not mounted
mount: wrong fs type, bad option, bad superblock on /cgroup,
...


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